NEJM: Transmission of SARS-CoV-2 in Domestic Cats

#15,259

Over the past couple of months we've looked at a number of field reports, and some limited research, on the susceptibility of cats (and other companion animals) to the COVID-19 pandemic and their potential for transmitting the SARS-CoV-2 virus to others. 

CDC: Pets & Other Animals and COVID-19

Netherlands: COVID-19 In Farmed Mink

APHIS: Confirmation of COVID-19 in Two Pet Cats in New York

WCS: A Tiger at Bronx Zoo Tests Positive for COVID-19

Six weeks ago, in Susceptibility of Ferrets, Cats, Dogs & Other Domestic Animals to SARS-CoV-2  by Hualan Chen et al., we looked at the experimental infection of a variety of farmed animals and household pets with the novel coronavirus. 

The authors wrote:

We found that SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and ducks, but efficiently in ferrets and cats. We found that the virus transmits in cats via respiratory droplets. 

Late yesterday the NEJM published a research letter from a team led by Yoshihiro Kawaoka - a professor at UW-Madison’s School of Veterinary Medicine - that confirms transmission of the SARS-CoV-2 virus among domestic cats. 

What isn't yet known is whether cats can transmit the virus on to other species - including humans - or if they can, how much of a role (if any) they might play in the spread of COVID-19.   

UW-Madison has provided a statement (excerpts below) summarizing the findings.

Study confirms cats can become infected with and may transmit COVID-19 to other cats

May 13, 2020 By Kelly April Tyrrell 

In a study published today (May 13, 2020) in the New England Journal of Medicine, scientists in the U.S. and Japan report that in the laboratory, cats can readily become infected with SARS-CoV-2, the virus that causes COVID-19, and may be able to pass the virus to other cats.

Professor of Pathobiological Sciences at the University of Wisconsin School of Veterinary Medicine Yoshihiro Kawaoka led the study, in which researchers administered to three cats SARS-CoV-2 isolated from a human patient. The following day, the researchers swabbed the nasal passages of the cats and were able to detect the virus in two of the animals. Within three days, they detected the virus in all of the cats.

The day after the researchers administered virus to the first three cats, they placed another cat in each of their cages. Researchers did not administer SARS-CoV-2 virus to these cats.

Each day, the researchers took nasal and rectal swabs from all six cats to assess them for the presence of the virus. Within two days, one of the previously uninfected cats was shedding virus, detected in the nasal swab, and within six days, all of the cats were shedding virus. None of the rectal swabs contained virus.

Each cat shed SARS-CoV-2 from their nasal passages for up to six days. The virus was not lethal and none of the cats showed signs of illness. All of the cats ultimately cleared the virus.

“That was a major finding for us — the cats did not have symptoms,” says Kawaoka, who also holds a faculty appointment at the University of Tokyo. Kawaoka is also helping lead an effort to create a human COVID-19 vaccine called CoroFlu.

The findings suggest cats may be capable of becoming infected with the virus when exposed to people or other cats positive for SARS-CoV-2. It follows a study published in Science by scientists at the Chinese Academy of Agricultural Sciences that also showed cats (and ferrets) could become infected with and potentially transmit the virus. The virus is known to be transmitted in humans through contact with respiratory droplets and saliva.

“It’s something for people to keep in mind,” says Peter Halfmann, a research professor at UW–Madison who helped lead the study. “If they are quarantined in their house and are worried about passing COVID-19 to children and spouses, they should also worry about giving it to their animals.”

Both researchers advise that people with symptoms of COVID-19 avoid contact with cats. They also advise cat owners to keep their pets indoors, in order to limit the contact their cats have with other people and animals.

Kawaoka is concerned about the welfare of animals. The World Organization for Animal Health and the Centers for Disease Control and Prevention say there is “no justification in taking measures against companion animals that may compromise their welfare.”

Humans remain the biggest risk to other humans in transmission of the virus. There is no evidence cats readily transmit the virus to humans, nor are there documented cases in which humans have become ill with COVID-19 because of contact with cats.

There are, however, confirmed instances of cats becoming infected because of close contact with humans infected with the virus, and several large cats at the Bronx Zoo have also tested positive for the virus.

(Continue . . . )

While we have no evidence of cat-to-human transmission of SARS-CoV-2, it is at least scientifically plausible.  Both species are susceptible to the disease, and cats have been shown to shed the virus.  

While rare, we've seen the transmission of at least one novel flu virus - avian H7N2 - from cats to humans at a NYC animal shelter (see EID Journal: Avian H7N2 Virus in Human Exposed to Sick Cats).

At the same time, previous concerns - going back the better part of two decades - over the infection and spread of avian H5 viruses by domestic cats (see EID Journal: HPAI H5N6 In Domestic Cats - Korea, 2016) have gone unrealized.

Because of these recent reports, the CDC has generated (and updated) guidance for pet owners, and anyone likely to come in contact with animals, for this COVID-19 pandemic. Note: This is a `work in progress' and the advice may change over time.

Pets and Other Animals

Credit CDC
Only a few pets have tested positive for the virus that causes COVID-19. Currently, the risk of pets spreading it to people is low. Learn more

Animals and COVID-19

If You Have Pets

If Your Pet Tests Positive

Guidance for Veterinary Clinics

In addition to these webpages, the CDC maintains an extensive COVID-19 FAQ (Frequently Asked Questions) list, including a section on COVID-19 & Animals.

For those looking for more information, the AVMA (American Veterinary Medical Association) maintains a detailed webpage on what is known about animal infection with the SARS-CoV-2 virus.

SARS-CoV-2 in animals

While the infection risk to, and from, animals is believed to be low at this time, the AVMA suggests:

Until more is known about this virus, if you are ill with COVID-19 you should restrict contact with pets and other animals, just as you would restrict your contact with other people. When possible, have another member of your household or business care for any animals, including pets while you are sick. If you have a service animal or you must care for your animals, including pets, wear a cloth face covering; don’t pet, share food, kiss, or hug them; and wash your hands before and after any contact with your pet, service animal, or other animals. You should not share dishes, drinking glasses, cups, eating utensils, towels, or bedding with other people or pets in your home.